Gene Regulation

What is the primary role of nucleic acids in the synthesis of proteins?

They act as information molecules that encode the specific instructions for protein synthesis.

Identify the three main forms of RNA involved in gene expression.

"The three main forms are messenger RNA (mRNA)

What does it mean for the genetic code to be described as 'universal'?

It means that the same specific codons code for the same amino acids in almost all organisms.

"The genetic code is described as _

meaning that more than one codon can code for the same amino acid."

What is the function of a triplet code in the context of the genetic code?

It is a sequence of three nucleotides that codes for one specific amino acid.

List the three main steps of gene expression in eukaryotic cells.

"The steps are transcription

"In eukaryotic gene structure

what is the role of introns?"

"In eukaryotic gene structure

what is the role of exons?"

What is the function of the promoter region in a gene?

The promoter is the specific DNA sequence where RNA polymerase binds to initiate transcription.

What is the function of the operator region in prokaryotic DNA?

"The operator is the binding site for transcription factors

How does the location of transcription and translation differ between prokaryotes and eukaryotes?

"In prokaryotes

Why can transcription and translation occur at the same time in prokaryotic cells?

"Because prokaryotes lack a nuclear envelope

Define constitutive genes.

These are genes that are continually transcribed and are always switched on.

How do induced or repressed genes differ from constitutive genes?

"They are initiated or stopped by transcription factors as needed by the cell

What is the primary function of regulatory genes?

"They code for transcription factors

What is the primary function of structural genes?

"They code for proteins or RNAs that are not involved in gene regulation

Define an operon.

An operon is a group of multiple structural genes controlled and transcribed together by a single promoter.

In which type of organism are operons primarily found?

Operons are found mainly in prokaryotes.

What amino acid does the $trp$ operon regulate the synthesis of?

Tryptophan

"The $trp$ operon is a _ operon

meaning its default state is 'on' but it can be switched 'off'."

How many structural genes are contained within the $trp$ operon?

"Five structural genes ($trpE$

Identify the two main mechanisms used to prevent tryptophan synthesis when levels are high.

Repression and attenuation.

"In the $trp$ operon

what does the regulatory gene $trpR$ code for?"

Describe the state of the $trp$ repressor when tryptophan levels are low.

"The repressor is inactive and unable to bind to the operator

What role does tryptophan play in the repression mechanism of the $trp$ operon?

It acts as a corepressor by binding to the repressor protein and activating it.

What is the physical effect of an active $trp$ repressor binding to the operator?

"It blocks RNA polymerase from moving along the DNA

What is the primary purpose of attenuation in the $trp$ operon?

It is a secondary control mechanism that prevents the completion of transcription when tryptophan levels are high.

Where is the leader segment (LS) located in the $trp$ operon?

It is located between the operator and the first structural gene ($trpE$).

Under what condition regarding the repressor does attenuation typically occur?

Attenuation occurs when the repressor protein is not bound to the operator region.

How many distinct regions exist within the leader mRNA of the $trp$ operon?

"Four regions (1

What specific feature in Region 1 of the $trp$ leader mRNA allows the ribosome to sense tryptophan levels?

It contains two adjacent tryptophan (UGG) codons.

"When tryptophan is high

where does the ribosome pause on the leader mRNA?"

"In the $trp$ operon attenuation mechanism

which two regions bind together to form the 'terminator' hairpin loop when tryptophan is high?"

How does the formation of the 3-4 hairpin loop lead to the termination of transcription?

"The loop pulls the mRNA away from the DNA template at the attenuator sequence

What is the attenuator sequence at the end of the leader region composed of?

A sequence of uracil ($U$) nucleotides.

What are the monomers that make up a polypeptide chain?

Amino acids

Define a proteome.

A proteome is the entire set of proteins expressed by an organism at a given time.

What is the role of the rough endoplasmic reticulum in protein synthesis?

It is involved in the folding and transport of proteins synthesized by attached ribosomes.

What is the role of the Golgi apparatus in a cell's protein pathway?

"It modifies

How do regulatory genes influence gene expression during transcription?

They code for transcription factors that bind to the promoter or RNA polymerase to induce or repress the process.

Why does eukaryotic gene regulation occur at more steps than prokaryotic regulation?

Because eukaryotes have a more complex expression process including RNA processing and nuclear transport.

"In prokaryotes

gene regulation occurs primarily during which stage of expression?"

What happens to the $trp$ repressor protein when tryptophan detaches from it?

"The repressor changes shape and becomes inactive

How do tRNA molecules contribute to the process of translation?

"They bring specific amino acids to the ribosome

Why are enzymes considered catalysts in biochemical pathways?

They increase the rate of chemical reactions without being consumed in the process.

What is the relationship between the 3-4 stem loop and the attenuator sequence in the $trp$ operon?

"The formation of the 3-4 loop puts tension on the weak hydrogen bonds between the adenine-uracil base pairs at the attenuator

Identify the location of the $trpR$ gene relative to the $trp$ operon.

It is located upstream of the operon.

"In prokaryotic gene expression

what structure is responsible for reading mRNA to produce a polypeptide?"

What defines the 'default' state of the $trp$ operon in $E. coli$?

The default state is 'on' because the repressor protein is synthesized in an inactive form.

List the sequence of events in the $trp$ operon when tryptophan levels are low.

1. Expression of $trpR$ gene; 2. Tryptophan detaches from repressor; 3. Structural genes are transcribed; 4. Tryptophan-producing enzymes are synthesised.

List the sequence of events in the $trp$ operon repression mechanism when tryptophan levels are high.

1. Expression of $trpR$ gene; 2. Corepressor binds to repressor; 3. Repressor blocks RNA polymerase; 4. Structural genes are not expressed.